test: test custom hash to field

backend/groth16/groth16_test.go

@@ -1,17 +1,56 @@
 package groth16_test
 
 import (
+	"fmt"
 	"math/big"
 	"testing"
 
 	"github.com/consensys/gnark"
 	"github.com/consensys/gnark-crypto/ecc"
+	"github.com/consensys/gnark/backend"
 	"github.com/consensys/gnark/backend/groth16"
 	"github.com/consensys/gnark/constraint"
 	"github.com/consensys/gnark/frontend"
 	"github.com/consensys/gnark/frontend/cs/r1cs"
+	"github.com/consensys/gnark/test"
 )
 
+func TestCustomHashToField(t *testing.T) {
+	assert := test.NewAssert(t)
+	assignment := &commitmentCircuit{X: 1}
+	for _, curve := range getCurves() {
+		assert.Run(func(assert *test.Assert) {
+			ccs, err := frontend.Compile(curve.ScalarField(), r1cs.NewBuilder, &commitmentCircuit{})
+			assert.NoError(err)
+			pk, vk, err := groth16.Setup(ccs)
+			assert.NoError(err)
+			witness, err := frontend.NewWitness(assignment, curve.ScalarField())
+			assert.NoError(err)
+			assert.Run(func(assert *test.Assert) {
+				proof, err := groth16.Prove(ccs, pk, witness, backend.WithProverHashToFieldFunction(constantHash{}))
+				assert.NoError(err)
+				pubWitness, err := witness.Public()
+				assert.NoError(err)
+				err = groth16.Verify(proof, vk, pubWitness, backend.WithVerifierHashToFieldFunction(constantHash{}))
+				assert.NoError(err)
+			}, "custom success")
+			assert.Run(func(assert *test.Assert) {
+				proof, err := groth16.Prove(ccs, pk, witness, backend.WithProverHashToFieldFunction(constantHash{}))
+				assert.NoError(err)
+				pubWitness, err := witness.Public()
+				assert.NoError(err)
+				err = groth16.Verify(proof, vk, pubWitness)
+				assert.Error(err)
+			}, "prover_only")
+			assert.Run(func(assert *test.Assert) {
+				proof, err := groth16.Prove(ccs, pk, witness)
+				assert.Error(err)
+				_ = proof
+			}, "verifier_only")
+		}, curve.String())
+	}
+}
+
 //--------------------//
 //     benches		  //
 //--------------------//
@@ -116,6 +155,27 @@ func referenceCircuit(curve ecc.ID) (constraint.ConstraintSystem, frontend.Circu
 	return r1cs, &good
 }
 
+type commitmentCircuit struct {
+	X frontend.Variable
+}
+
+func (c *commitmentCircuit) Define(api frontend.API) error {
+	cmt, err := api.(frontend.Committer).Commit(c.X)
+	if err != nil {
+		return fmt.Errorf("commit: %w", err)
+	}
+	api.AssertIsEqual(cmt, "0xaabbcc")
+	return nil
+}
+
+type constantHash struct{}
+
+func (h constantHash) Write(p []byte) (n int, err error) { return len(p), nil }
+func (h constantHash) Sum(b []byte) []byte               { return []byte{0xaa, 0xbb, 0xcc} }
+func (h constantHash) Reset()                            {}
+func (h constantHash) Size() int                         { return 3 }
+func (h constantHash) BlockSize() int                    { return 32 }
+
 func getCurves() []ecc.ID {
 	if testing.Short() {
 		return []ecc.ID{ecc.BN254}